Repetitive nerve stimulation (RNS) of the trapezius muscle at slow rates was performed on 192 patients with amyotrophic lateral sclerosis (ALS). Fifty‐six patients (29%) showed classical neuromuscular decrement of 10–43% (mean 16.8%) while 44 patients (23%) had a borderline decrement of 5–9%. The trapezius was significantly more sensitive in revealing the defect than the distal hypothenar muscles. In 30 patients followed serially, the decremental response remained constant or increased with time. However, 25% of patients continued to show no decrement in spite of progression of disease. No statistical correlation was found between decrement and clinical severity, disease staging, or disease progression. The finding that at least 50% of ALS patients show some degree of decrement on RNS of the trapezius muscle suggests that functional alterations of the neuromuscular junction accompany this disease. © 1994 John Wiley & Sons, Inc.